Are you looking for numbers or an approximation? If the former, I suggest you mention a particular hub.
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Neil FeinAug 26 '10 at 5:17

2

Weight should not affect efficienty, which is a measure of energy input vs. energy output. A bike can be heavy (require more energy to move), and even so be efficient (not wasting energy with friction, flexing, etc.)
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heltonbikerNov 23 '11 at 2:34

I think he's saying that both lower efficiency and higher weight will "lose in performance", which is true, assuming a route that isn't totally flat and isn't almost all downhill.
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armbMay 8 '13 at 13:01

7 Answers
7

It is easy to keep a hub gear running well for years, but an unmaintained derailleur will become inefficient very quickly. A hub gear allows the chain to be fully enclosed, for all but the most dedicated cyclist; an enclosed chain will be more efficient as it will be cleaner and better oiled.

An enclose chain allows you to arrive at work, with clean cloths and no need to change, this can save lots of time. Not having to spend time adjusting a derailleur or cleaning your chain also increase the efficiency of your life.
However it takes longer to remove the wheel if you have hub gears and an enclosed chain.

Personally I think on a road bike:

Hub gears are more efficient if you wish to use a bike to make lot of short trips as part of your day to day life.

But derailleurs are more efficient if you consider going fast on a bike to be very important and are willing to put the work into the bike that is needed to keep it in a very good state of maintenance.

It depends on the model you get, but the efficiency is generally comparable. Derailleurs that are in really good condition and properly lubed will be more efficient, but marginally, and will often be less efficient due to real world conditions.

I have one road bike with a 3x9 derailleur, a smaller bike with a 7 speed nexus, and a brompton that actually has a hub AND a derailleur for a low/high gear. The other considerations (tire size, pressure, etc) probably matter far more than the gear. For easy shifting and maintenance, hubs, no question.

Newer hubs are generally considered more efficient (Shimano Alfine vs Nexus, that sort of thing). Also, Shimano has an 11 speed coming out that has a different type of lube than usual, and is supposed to have improved efficiency, but I don't think we'll know much till its out.

Then there's the Rohloff. Way too expensive to buy, but shows what a good hub can pull off:

I own a Rohloff and don't think it is way expensive to buy. Not only it costed the same as the parts I didn't have to buy (crankset, rear and front deraileur, cogset, shifters, etc.), but also the drivetrain lasts longer. It is not perfect, but it is worth for anyone that will crush the miles from it.
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heltonbikerNov 23 '11 at 2:38

In 2001, Kyle and Berto published a comparison of the mechanical efficiency of several configurations of derailleur and internally-geared hubs in Human Power, which you can find here. Among the systems tested were a Shimano MTB derailleur system, a Sturmey-Archer 3-speed hub, the Shimano 7-speed Nexus hub, and the 14-speed Rohloff hub. MTB derailleur systems are (now) known to be less efficient (more lossy) in terms of power transmission than "road bike" derailleur systems. In particular, note fig. 12 in the cited link, which compares average efficiency at three different levels of power for the internally-geared and MTB derailleur system. Spicer (2000) has measured the power transmission efficiency of an ideal chain driven system at about 98%, so that is what you would expect the maximum efficiency to be.

In general, it depends on the hub and the cyclist. My gut and my experience with the two 3-speed hub geared bikes I own (SRAM and Nexus hubs) suggests to me that not much in the way of pedaling energy is sacrificed.

Let's say, in The Netherlands were the majority of bikes are used as a means of personal transportation the vast majority of gears are hub gears. The main reason is their very low maintenance, and of course the fact that you get a proper chain cover. For use as means of transportat

I can only compare the basic Shimano Acera and Deore (3x8) deraileurs to the Rohloff 14-speed hub, but these are my observations relating to efficiency. There's a distinction here between pedalling efficiency and gear-shifting efficiency. I'm going to mention both as I don't know which one you meant.

On the Rohloff hub

In the majority of gears it doesn't feel like there's any loss of pedalling power compared to a direct-drive fixed gear bike (subjective, I know). Gears 7 and 12 make some noise and seem a little less efficient.

Changing gears is always impossible if significant force is on the drivechain.

A short pedalling pause is required to shift gears.

It is possible to change to/from any gear when stationary or coasting.

Gear inches change between gears is simple and predictable (roughly the same percentage per click).

On a derailer

A small amount of pedalling power seems to be lost to the jockey wheel. This is significant only if it gets dirty or one of the shifters is misaligned. Several gears are noisy/inefficient due to chain angle.

Changing gears is sometimes tricky if there a large force on the drive chain. It depends on which change is being made, some are really easy and smooth, others need some care.

No pause to fast, gentle pedalling is required to shift gears.

Only possible to change gears when pedalling.

Two shifters means that shifting quickly to a predictable-length gear a skill that requires a bit of thought.

YMMV, but I find the Rohloff to be efficient and simple to use. We use it on a tandem, so it may be that the pause needed when shifting is less distruptive on a solo bike.

However, I also expect that an experienced racer would be able to shift their high-spec gears much more quickly and efficiently than any hub gears and that this might mean that deraileurs are the only option for racing. That and the fact that you can't seem to connect them to brifters.

In my ~1 month experience with the Deore (11 speed?) internally geared hub compared with well-maintained derailleur systems of comparable quality and newness, the internally geared hub has a noticeable amount of internal loss. Note that this test was carried out about a year ago. I ended up returning the bike.

First test (idle loss): turn the crank a few times and get the wheel to spin, see how long it continues to spin. This will tell you how much energy is lost in the hub. In my experience the loss is noticeable.

Second test (loss under power): using a similar gear ratio, turn the crank at a fixed speed for about a minute, you will get an idea of how much energy input is needed to keep the wheels turning at a fast, steady pace. Compare the two energy inputs.